a. Field of the Invention
This invention relates generally to an assembly of parts of different materials which are plated simultaneously and to a method of fabricating such an assembly, and more particularly to a method of preparing an assembly consisting of a plurality of parts of different materials, which parts are attached together before plating such an assembly and to an article fabricated in accordance with such a method.
B. Prior Art
When two or more parts of different materials which require plating are to be attached together in an assembly, it has generally been the practice in the past to fabricate, machine, and plate each part separately before assembling such parts. It has been considered impossible in the past to simultaneously plate certain different or dissimilar materials. Consequently, if two or more parts of an assembly are made of such incompatible materials, the only course available is to have each part fabricated, machined, and plated separately before assembly thereof.
It can be readily appreciated that if two or more parts of an assembly which are made of incompatible materials can be plated together, rather than separately, a number of distinct advantages are realized. If a plurality of parts can be assembled before being plated, it is generally possible to machine those parts as an assembly, thereby reducing the number of machining steps, the time required to perform the machining operation, and the cost of machining. In some instances, it is also possible to eliminate one or more machining steps which would be required if the parts are machined separately.
A considerable savings is realized in the plating process, since the time for preparing and plating the parts as an assembly rather than as separate parts, is considerably reduced. Furthermore, if two or more parts are plated as an assembly, the mating surfaces thereof need not and will not receive any plating material, thereby reducing the cost of plating materials needed in the plating process.
Another advantage is gained if it is possible to machine two or more parts as an assembly, rather than separately and before they are attached together. If two parts are machined separately, it is obvious that a relatively great degree of accuracy in their relative positions after they are assembled cannot be attained without a considerable amount of time and effort and the use of a sophisticated equipment. However, if two parts are machined after they are assembled, the common machined surfaces thereof will be accurately positioned with respect to one another within the tolerance of the machine operation. Of course, the tolerance of a machine operation is generally much less than the tolerance which can be attained by positioning two previously machined parts with respect to one another and securing the two together.
In some instances, it is possible to employ a different and better means of attaching two parts together if such parts are attached before they are plated. For example, it may not be possible to employ a bonding agent to attach two parts together after they have been plated separately. It can also be appreciated that the means employed for attaching two parts together must be capable of permitting the two parts to be positioned relative to one another if the machining operation is performed first.
It can be appreciated, therefore, that a considerable savings and a more superior product can be realized if two or more dissimilar metals can be joined together during the machining and plating operations. That is, if such a unitary article can be made of two or more such dissimilar metals, which then can be machined, cleaned and plated as a unitary article, manufacturing costs are reduced considerably and permissible tolerances can be achieved more easily.
If the dissimilar metals are steel and aluminum, it has always been considered an impossibility in the past to employ the same cleaning and activating agents for such metals in preparing them for paint. More particularly, the cleaning agent for steel tends to remove the metallic elements from the aluminum alloy leaving a layer of residue in the form of smut. It was considered impossible in the past for any nickel plating adhesion to occur over this layer of smut. Also, the cleaning agent normally employed for aluminum tends to attack the steel.
It has been the practice in the past to prepare an aluminum die cast member as follows: (1) machine the member to permissible tolerances; (2) vapor degrease with the vapors of trichloroethylene for a period of 3 to 5 minutes; (3) clean the member with a heated caustic solution to remove surface metal for a period of 30 seconds to 5 minutes and then rinse with water; (4) remove the remaining smut with nitric acid or a bifluoride salt for a period of 30 seconds and then rinse with water; (6) repeat steps 3-5 as often as necessary to clean the member; (7) dip the member in a zincate solution for a period of 2 minutes and then rinse with water; (8) plate the member, such as with electroless nickel plating.
It has been the practice in the past to prepare a steel member in accordance with the following process: (1) machine or grind to permissible tolerances; (2) vapor degrease with heated trichloroethylene for a period of 3 to 5 minutes; (3) clean with a heated alkaline solution and a six volt direct current potential for a period of 3 to 5 minutes and then rinse with water; (4) remove smut from the member by contacting it with muriatic acid for a period of 3 to 5 minutes and then rinse with water; (5) repeat steps 3 and 4 as often as necessary to clean the member; and (6) thereafter plate the member, such as with electroless nickel plating.
After two such parts have been prepared in accordance with the above, they are attached together, such as by bolts, to form a unitary article. It can be appreciated, however, that the necessity for machining each member separately reduces the degree of accuracy which can be obtained in the final position of the two members with respect to one another. Furthermore, it can be appreciated that the machining and plating of two members independently is considerably more costly than the machining and plating of a unitary article formed of two such members joined together.